Due to the nature of offset printing (need to print with the participation of water, the printing plate and the blank are almost on the same plane), the offset ink must have good water resistance, good adhesion, elasticity, and very good touch. transsexual.
1 water resistance. For smooth printing, it is necessary to select inks with good water resistance, but unlike other conditions, the water resistance of offset inks is not as strong as possible. Completely water-repellent offset inks cannot be printed on the machine. This is due to the fact that during the ink transfer process, water that has reached the ink path due to the high-speed shearing of the printing press will inevitably be encountered. When the oil and water are completely incapacitated, the normal ink transfer will be hindered.
· In printing, in order to ensure the ink's water resistance, we add additives (desiccant, remover, varnish, anti-fouling agent, etc.) to the ink to avoid reducing the cohesion of the ink, and in some cases According to the situation, a tackifier is added to the ink to restore the cohesion of the ink so as to restore the ink's water resistance. At the same time, the ink in the ink path and the ink fountain should be regularly cleaned to prevent the use of the residual ink on the machine and affect the water resistance.
2 sticky and elastic. Good adhesion is the premise to ensure that the ink can be properly transferred and transferred; and the ink's elasticity can ensure that the ink can quickly recover and level after transferring to the surface of the substrate. Good elasticity is the prerequisite for ensuring the smoothness of the surface of the printing dot.
• As mentioned above, except that good quality inks are selected, what we do in printing is to maintain the properties of inks. Many additives are added as mentioned above to minimize the ink properties due to human operations The change. Also pay attention to the control of the wetting fluid (discussed in detail in the process).
Thixotropic. The ink used in offset printing must have good thixotropy, that is, the fluidity increases under the action of the mechanical shear force when the ink passes out of the ink fountain, and the mechanical force when the ink is transferred from the surface of the blanket to the surface of the substrate. The disappearance of ink, the rapid decline in the flow of ink, began with the penetration of the binder in the ink on the surface of the substrate together to promote the initial curing of the ink. This process is very important for multi-color printing, can greatly affect the multi-color machine's overprint effect.
• Choosing a good thixotropic ink is very important for printing.
4 ink transparency. Offset inks require good transparency.
In fact, the transparency of printing inks in printing cannot be guaranteed, and the transparency of inks of different colors is not always the same. Therefore, in the printing process, the color sequence of the ink should be considered. A reasonable arrangement of the color sequence can effectively improve the color saturation of printed materials. degree.
5 ink particle size and coloring. Good printing inks require that the finer the particles of the ink pigment, the better the coloring properties. Select ink must not ignore these two points, the same is still the old saying, in the cost allowable conditions to select the finest particles of ink, high colorability of the ink, are conducive to print quality control.
6 ink stability. The stability of the ink includes the ability of the ink to resist light, heat, acid, alkali, and alcohol, and it requires that the ink does not change color and age under certain conditions, especially for inks with special uses (such as printing on billboards that need to be displayed in the sunlight, etc.) ), it is even more demanding that inks have this special resistance.
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